We describe a new pathway signaling neutrophil (PMN) influx and damage to the airways that may play a role in chronic obstructive pulmonary disease (COPD). Chemical or enzymatic breakdown of collagen releases a tripeptide, PGP, and an acetylated form (N-?-PGP) that are chemotactic for PMN. Prolonged airway exposure to this peptide causes alveolar enlargement and right ventricular hypertrophy. Further- more, PGP is found in the airways of animals exposed to aerosolized endotoxin (LPS) and markedly contributes to PMN influx. The enzymatic production of PGP is a stepwise process initially involving matrix metalloproteases (MMP)-8 and/or MMP-9 with prolyl endopeptidase (PE), a serine protease, catalyzing the final reaction. We have also found that PGP is present in bronchoalveolar lavage fluid (BALF) and/or sputum from most COPD patients but not controls or asthmatics. Sputum from COPD patients but not control individuals also contains all the enzymatic machinery necessary for the ex vivo generation of PGP from purified collagen and such PGP production can be blocked by MMP-8 or MMP-9 inhibitors or by a PE- specific inhibitors. The macrolide trial currently being conducted by the COPD Clinical Research Network (CRN) offers a unique opportunity to study the role of PGP in airway inflammation in COPD. Measurement of PGP and N-?-PGP in the cohort of COPD patients recruited for this trial will provide information which could otherwise only be acquired by another large-scale clinical trial. The current period of enrollment for this trial affords an important window of opportunity, belying the time-sensitive nature of this proposal. Measurement of MMP and PE levels and activity in sputum will provide new and important information on the generation of PGP in COPD and identify possible new therapeutic targets against airway inflammation in this disease. Importantly, macrolide antibiotics have been identified as negative transcriptional regulators for MMPs. This is proposed to underly a possible therapeutic activity in chronic lung diseases such as COPD. Finally, this trial will enable us to test this hypothesis in a large cohort of COPD patients, both taking azithromycin and controls, thereby providing a scientific basis for the activity of macrolides in COPD. Our underlying hypothesis is that levels of N-?-PGP/PGP and the activity of enzymes that generate them, specifically MMPs and PE, are lower in patients with COPD taking azithromycin than in COPD patients on placebo and that this reduction will correlate with improvement in clinical endpoints in these patients. Specific aims: 1. Measure levels of N-?-PGP/PGP and activity of PGP-generating enzymes, specifically MMP's and PE, in sputum of COPD patients taking azithromycin and in sputum of COPD patients taking placebo. 2. Compare the ability of sputum from COPD patients taking azithromycin to generate N-a- PGP/PGP ex vivo from collagen with sputum from COPD patients taking placebo. 3. Correlate levels of N-?-PGP/PGP and activity of PE in induced sputum with levels and activity in serum of COPD patients. COPD is now the fourth leading cause of death in the U.S. and is expected to be the third by 2020. This disease causes much human suffering as well as a large monetary burden. An understanding of COPD that leads to successful therapeutics has been hampered by a lack of biomarkers to diagnose and use as endpoints in clinical trials as well as a lack of a fundamental understanding of the disease process itself. If successful, the current proposal will yield fundamental insights into the disease process and a new and specific biomarker for COPD as well as suggesting new therapeutic targets. (End of Abstract)